Vertical flow constructed wetlands for the treatment of inorganic ...

Sulfate reduction occurs under anaerobic conditions (lactate and acetate as
substrates):
2 CH3CHOHCOO - + SO4 2- + H + � 2 CH3COO - + 2 CO2 + 2 H2O + HS - (2.6)
CH3COO - + SO4 2- + 2 H + � 2 CO2 + 2 H2O + HS - (2.7)
Methanogenesis occurs in anaerobic conditions (acetate as substrate or CO2 reduction):
CH3COO - + 4 H2 � 2 CH4 + H2O + OH - (2.8)
4 H2 + CO2� CH4 + 2 H2O (2.9)
The contribution of each process to carbon removal is variable and will depend
on the nature of the wastewater and the type of constructed wetland, for example in
FWS wetlands all process may occur in similar proportions, aerobic respiration near the
surface and in the water column and anoxic/anaerobic reactions on the bottom and
sediments. In HF wetlands oxygen transfer is negligible, therefore it is likely that anoxic
and anaerobic reactions will prevail. In unsaturated VF wetlands, however, aerobic
processes dominate.
2.4.2 Nitrogen (N)
Nitrogen is an essential nutrient for all living organisms, being present in the
form of proteins, nucleic acids, adenosine phosphates and pigments. (Hagopian and
Riley, 1998). Yet, nitrogen compounds are among the main pollutants of concern in
wastewater because of their role in, (among with other nutrients such as phosphorus)
contributing to eutrophication, favouring algal blooms, and depreciation of dissolved
oxygen levels in receiving water bodies. Furthermore, unionised ammonia (NH3) and
nitrite (NO2 - ) are toxic to fish and other aquatic organisms in low concentrations. In
water and wastewater the most important inorganic forms of nitrogen are ammonium
(NH4 + ), NO3 - , NO2 - , and dissolved nitrogen gas (N2). Organic nitrogen compounds in
wastewaters originate from food, faeces and urine, these high molecular weight
compounds (proteins, urea, amino acids) are proteolised and deaminated to ammonia.
The overall multi step biochemical process by which ammonia is released from
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